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Old 10-03-2016, 10:05 AM
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thegableguy (Chris)
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Advantages of Go-To over dual axis drive

Hi there,

After several very happy months with a Dobsonian I'm keen to get a new rig specifically for beginner AP (having exhausted the possibilities using my pro-level DSLR & 2x Barlow through the Dob).

After much discussion in these and other pages, I've decided a motorised mount is the next purchase. When I master using it with a 200mm lens, I'll get something like the standard ED80 and go from there.

Being a cheapskate I'm looking to spend maximum $1k. Ideally I'd get a HEQ5 Pro, but the cheapest I can find is $1300 plus postage. I'd take an EQ5 Pro for around $800 but again no-one's selling any.

So, I was wondering... how would I go with spending about $750 on an EQ5 tripod and $250 on dual motor drives? How lucky would I have to be with my polar alignment to get 3-min subs at 600mm?

Am I vastly better off saving a while longer and going the Go-To option? Is it not even worth considering going the cheaper dual axis route? Or is it actually quite possible to get decent results using such a system (without first having attained a Masters degree in astrophysics)?

Any advice appreciated!!

Cheers
~C
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Old 10-03-2016, 10:23 AM
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The Mekon (John Briggs)
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Used HEQ5s go for around $800 on the classifieds this forum. Wait until one comes up.
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Old 10-03-2016, 10:35 AM
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thegableguy (Chris)
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Is it worth putting up a WANTED ad for one? A used HEQ5 Pro is exactly what I'm after.
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Old 10-03-2016, 11:40 AM
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Diy?
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Old 10-03-2016, 12:14 PM
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The_bluester (Paul)
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Goto is only useful for locating objects more easily, you still need a good polar alignment to avoid field rotation in the images.

If you are quite happy to hunt manually for your targets then goto is essentially a non event. The only difference between goto and basic tracking is that with goto you have electronics in/on/connected to the mount which (After alignment) know where the mount is aimed and so can automatically aim it at targets. If your polar alignment is way off you will still have field rotation effects in images.
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Old 10-03-2016, 12:46 PM
raymo
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That's simplifying things Paul. With a good 2 star alignment, and having
verified that the Go To is putting a target in the F.O.V. you can find
targets that are too faint to see by taking a short exposure. You can then
centralise the target, and off you go. When star hopping, or working with
setting circles you've got to be lucky to get a very faint target into your F.O.V. at all, and can spend ages trying to locate the target. Another thing is that Go Tos have a polar alignment routine built into them, obviating the need to grovel about using the polar scope when doing visual.
raymo
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Old 10-03-2016, 01:42 PM
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The_bluester (Paul)
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Do the lower priced goto mounts do the polar align routines? I have always been leery about them to be honest as they seem often (By the number of threads about the subject) to be quite flaky and produce unpredictable results. By the time we are talking about imaging with an ED80 I would hazard a guess we are then looking down the barrel of a guider package, typically meaning drift alignment with the likes of PHD.

I see the two issues as fairly separate. Goto will find you targets and may come with polar align routines (Which I am not sure how accurately you will be able to do with a 200mm lens on a camera) but it is possible to fettle polar alignment without them and for image quality, accurate polar alignment is likely to be the biggest issue, goto will get you on the target but unless you get the PA right you will have field rotation regardless.

I would say if you can afford it, get the best mount you can. buying the smallest and cheapest one that will do the job you are doing right now often ends up in disappointment. The first upgrade often seems to trigger a round of upgrades after that.


Sounds a lot like my race car actually. more power led to bigger and stickier tyres which meant new and expensive rims which meant more cornering force which meant suspension changes which led to higher corner speeds and even more force and higher speeds on the straights which let to beiger brakes which led to getting rid of the standard brake master cylinder and booster and fitting race pedals with bias control etc etc etc etc. The last half a second around my favourite track has cost me about ten grand!


I seem to have two expensive hobbies!
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Old 10-03-2016, 03:57 PM
raymo
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I generally work at 1000mm [the focal length of my 8" f/5 Newt]. If I take the time to get the best P.A. the mount can give me, and don't go
on to a drift align afterwards, I can usually get about 75% useable subs
at 75 secs, and about 90% at 60 secs. If I do a drift as well, I can about
double those figures. From these figures you can see that at 200mm
that would give around 4 to 5 minute subs, and much longer with a
drift alignment. I can get 150 secs with my 80mm f/5, and 270 with a drift. It also has a periodic error correction function. You can of course run the mount from a laptop too. I think all equatorial Go To mounts have a P.A. function.
The HEQ5 is the work horse for many imagers, along with its bigger
brother the NEQ6. We can't all afford 5 or 10 thousand dollar mounts,
which are in any case not immune to problems.
raymo
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Old 10-03-2016, 05:12 PM
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I have an ED80 on EQ5 with dual axis drive. You will never get 3min exposure unless you have guiding (not GOTO). After spending few hours aligning it, if lucky, I could get 90s exposure (without guiding). Once I had 2 min but over half of the shots were not good. Even 90s requires luck.

The dual axis drive motors are rubbish for AP. They have large backlash as they have about 100x gearing inside. You press the RA back button on the hand controller and for a good second or two nothing happens... then you see the star moving. Initially I thought my hand controller was broken. I have not tried it but I don't think guiding will work well with them.

If you get EQ5 I would recommend not getting the dual axis drive but to build your own belt-driven drive. Cheaper and much better. I am just about finished making mine, just waiting for a clear night to take everything out and give it a first test. I am planing doing a writeup once I test everything if you are interested.

Another thing is that thanks to the high gearing, even if you build/get a GOTO system for the dual axis drive, it will be SLOWWWWWW. 15min between star hopping SLOWWWWWW.

Make sure you read this regarding EQ5 and dual axis motors. For GOTO, 1,2,3-star alignment etc I am using OnStep.


However, if you are after longer subs you will need have guiding. GOTO will only help finding objects in the sky. The cheapskate method is to use a finderscope with a webcam. I have also built one of those but I still have not given it a test. Changing too many things at once...

Anyway, get HQ5 if you can or be prepared to do some work improving the EQ5.

edit:
You can find 2nd hand dual-axis drives relatively cheaply.
Building your system will cost you a bit less than the new dual-axis drive, apart from your time. And you will learn a lot.

Last edited by luka; 10-03-2016 at 05:24 PM.
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Old 10-03-2016, 05:39 PM
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thegableguy (Chris)
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Quote:
Originally Posted by luka View Post
I have an ED80 on EQ5 with dual axis drive. You will never get 3min exposure unless you have guiding (not GOTO). After spending few hours aligning it, if lucky, I could get 90s exposure (without guiding). Once I had 2 min but over half of the shots were not good. Even 90s requires luck.

The dual axis drive motors are rubbish for AP. They have large backlash as they have about 100x gearing inside. You press the RA back button on the hand controller and for a good second or two nothing happens... then you see the star moving. Initially I thought my hand controller was broken. I have not tried it but I don't think guiding will work well with them.

If you get EQ5 I would recommend not getting the dual axis drive but to build your own belt-driven drive. Cheaper and much better. I am just about finished making mine, just waiting for a clear night to take everything out and give it a first test. I am planing doing a writeup once I test everything if you are interested.

Another thing is that thanks to the high gearing, even if you build/get a GOTO system for the dual axis drive, it will be SLOWWWWWW. 15min between star hopping SLOWWWWWW.

Make sure you read this regarding EQ5 and dual axis motors. For GOTO, 1,2,3-star alignment etc I am using OnStep.


However, if you are after longer subs you will need have guiding. GOTO will only help finding objects in the sky. The cheapskate method is to use a finderscope with a webcam. I have also built one of those but I still have not given it a test. Changing too many things at once...

Anyway, get HQ5 if you can or be prepared to do some work improving the EQ5.

edit:
You can find 2nd hand dual-axis drives relatively cheaply.
Building your system will cost you a bit less than the new dual-axis drive, apart from your time. And you will learn a lot.
Wait, wait, wait. You can't just disengage the drive motors and slew it around yourself? Good grief, why would someone design such a horrible system???

Building something might come later. I'd like to think I could. But I've never even seen an EQ mount in real life, let alone pull one apart and gut its electronic innards. Way too advanced for a humble Dobsonian owner.

Anyway, all food for thought. I think I might just sit on my savings for a while until a reasonably priced HEQ5 comes on the market - or, failing that, I can afford a new one. Many people seem to use a HEQ5 with great success, and it's somewhat future proofed against the inevitable upgrade. I like the look of the new GST truss tunes arriving next month; one of those atop a HEQ5 would look great in my studio...
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Old 10-03-2016, 06:08 PM
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The_bluester (Paul)
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Very few mounts at the lower end of the scale will retain alignment of the electronics after a manual slew. I bought an Orion Atlas Pro (Skywatcher AZEQ6 with a coat of black paint) specifically because it has encoders both on the motors and on both axis so that you can loose the clutches and point manually without the goto alignment being lost.

If you are happy to find targets manually it is not much of an issue on an EQ mount to not have the on axis encoders but an Alt-Az no longer knows where it is pointed if you release the clutches and tracking is lost as well as goto.

The Skywatcher AZEQ5 presumably has dual encoders like the AZEQ6? I am sure there are others but the AZEQ variants are the ones I am familiar with.
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Old 10-03-2016, 08:47 PM
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barx1963 (Malcolm)
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Paul
The AZEQ5 does have duel encoders.
In answer to cablesguys query about why they designed such a horrible system, simpley that it makes it more expensive and very rarely would you need to manually move the mount.
With my AZEQ6 the only time I have disengaged the clutch was to tweak the balance, other than that I always use go to with it, and this is from a guy who has used dobs for years!!

Malcolm
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Old 10-03-2016, 09:10 PM
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Which is sort of funny given I went the opposite way. I got a serious case of the irrits with the CPC telescope mount as I wanted to be able to slew manually while still having tracking in Alt-Az mode and bought the AZEQ type mount specifically because I could manually point and maintain alignment.

I point manually all the time and in EQ mode often don't even bother doing the star alignment. For visual use and quite apart from convenient EP positioning I find Alt-Az much nicer to aim near the pole, pointing an EQ there is a pain manually or using the slew buttons and anything near the pole will always be in that painful spot to point to. In Alt-Az while pointing at the zenith is a similar issue to an EQ at the pole (Like Dobsons Hole) all you have to do is wait an hour and the target becomes convenient again.
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Old 10-03-2016, 09:22 PM
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thegableguy (Chris)
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..... Yeah, wow.

You guys could easily be speaking Greek for all I understand of what you're saying. Clearly there's vastly more to this caper than buying a mount, pointing it somewhere near the southern pole, and sticking an OTA & camera on it.

Happy to say that it only makes me more excited about getting started. I really am very very keen to get cracking!

So, where did we end up, exactly? Heq5 still the way to go if I don't have much to spend but don't want to end up going backwards due to insufficient gear?
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Old 10-03-2016, 10:10 PM
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I don't have an inconvenient position with my 8" Newt, as I did a D.I.Y.
mod so that I can turn the OTA to whatever position I want, which is great, as my DSLR doesn't have a tiltable LCD screen.
Like Malcolm, I never slew manually.
raymo
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Old 10-03-2016, 11:23 PM
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Quote:
Originally Posted by thegableguy View Post
Wait, wait, wait. You can't just disengage the drive motors and slew it around yourself? Good grief, why would someone design such a horrible system???

Building something might come later. I'd like to think I could. But I've never even seen an EQ mount in real life, let alone pull one apart and gut its electronic innards. Way too advanced for a humble Dobsonian owner.

Anyway, all food for thought. I think I might just sit on my savings for a while until a reasonably priced HEQ5 comes on the market - or, failing that, I can afford a new one. Many people seem to use a HEQ5 with great success, and it's somewhat future proofed against the inevitable upgrade. I like the look of the new GST truss tunes arriving next month; one of those atop a HEQ5 would look great in my studio...
Sorry, I did not express myself correctly. You can manually slew the mount to wherever you want. But if you build a GOTO system with the dual-axis drive, you are limited to whatever speed the drive motors will do and they are SLOW. You can still manually slew the mount but if you do that the GOTO system will not know where you are any more.

Also EQ5 does not have any electronics inside.

My advice, unless you want to spend lots of time messing around, get HEQ5.

Alternatively, and someone else may be of better assistance here, you can get a bigger mount and put your dob tube on it. That way you can spend more money on the mount as you don't need to purchase ED80 later on.
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Old 11-03-2016, 07:52 AM
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I think the HEQ5 is a happy medium. The only thing it lacks compared to the AZEQ mounts (unless you really want to use Alt-Az mode) is the dual encoders to allow manual slewing without having to redo alignment and it is obviously cheaper than an EQ6.

In just depends on how far down the slippery slope of AP you slide, the next step usually seems to be a 6 and it just goes on from there.
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Old 11-03-2016, 09:52 AM
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Yeah. I'd love an NEQ6 but the funds just aren't there. They're not really there for a HEQ5 to be honest but sometimes a man just has to take back control of the household funds and deal with the consequences... can't decide whether to buy flowers or a helmet on my way home from the telescope shop...

Thinking I'll wait a month and if there aren't any secondhand HEQ5s available I'll just bite the bullet and get a new one.

Had a look at the HEQ5 specs and it has 800x slewing speed. Makes a lot of sense, maximum time between objects would be about a minute. I didn't realise that the attach-yourself motor drives only have 8x maximum!! Takes an hour to get from one side of the sky to another!! Ain't nobody got time for dat.

Can someone explain what the purpose of 0.25x, 0.5x and 0.75x speeds is? I can't imagine a scenario where they'd be of use...?
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Old 11-03-2016, 10:24 AM
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IMO they would only really be useful for guiding by hand if they are slew speeds rather than tracking speeds.
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Old 11-03-2016, 12:28 PM
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When using an autoguider you choose one of those very slow rates
[x.25 x.5 x.75 etc:] as the autoguider correction speed.
This can vary for several reasons, such as how good your P.A.
is, and the focal length of the imaging and guiding scopes, also
whether you are imaging near a pole or near the celestial equator.
raymo

Last edited by raymo; 11-03-2016 at 12:34 PM. Reason: more text
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